Modern manufacturing equipment relies on various resource or facility inputs in order to operate. For example, electricity is directly or indirectly required to run most, if not all such machinery. In addition, many machine processes require additional facilities such as compressed gas or air, vacuum pressure, and chemical, hydraulic, and aqueous flow to name a few. These facilities are the direct or indirect product of conventional expendable resources (e.g., electricity, gas, water). Accordingly, it is economically and environmentally advantageous to conserve or minimize usage of these facilities. While the present invention is applicable to conserving most any facility, it is primarily directed to conservation of liquid flow and, more particularly, water flow to a semiconductor wafer grinding machine. The remainder of this discussion will focus on the same.
In conventional wafer grinding, a wafer having a front side covered with a protective layer is placed on a vacuum chuck. The back side of the wafer is then brought into contact with a grinding wheel. As the grinding wheel passes over the wafer, it removes a thin layer of wafer material. Due to the frictional engagement of the grinding wheel with the wafer, heat is produced. To cool the wafer and the surrounding tool surfaces, a liquid coolant system is typically included. The coolant system provides directed flow of municipal or de-ionized water over the various components including the wafer and grinding wheel, thus maintaining a consistent temperature. In addition to cooling, the coolant rinses away the wafer material removed by the grinding wheel.
To monitor the amount of material removed from the wafer, the grinding machine also includes sensors or transducers that constantly monitor wafer thickness. It is critical that these sensors deliver accurate data throughout the grinding operation. Unfortunately, the output from these transducers is highly influenced by changes in temperature. To ensure accurate and repeatable data, the sensors are calibrated and operated within a narrow temperature range. Outside that range, sensor accuracy becomes unreliable. Accordingly, it is important to maintain the wafer thickness sensors at a consistent temperature throughout the grinding process.
During operation, the grinder typically grinds wafers continuously for a period of time. When grinding is complete, the machine enters a non-operational or "idle mode" at which time no wafer processing is occurring.
To conserve water, the coolant water flow may be shut off during idle mode. Unfortunately, when water flow is discontinued, the temperature of the sensors (and the other tool surfaces) changes. As discussed above, temperature variation has an adverse effect on sensor accuracy. Furthermore, the time required to bring the grinder back to operating temperature once water flow is restored may be extensive due to the size and mass of the machine.
Another problem with discontinuing the water supply to the grinder is that waste material not yet removed at the completion of the grinding operation may still be present. That is, material removed from the last processed wafers may not be completely rinsed from the grinding station at the time it enters idle mode.
To preserve sensor accuracy, eliminate "warm-up" time, and keep the grinder clean, some grinders apply a continuous water spray even during idle mode. While this assures consistent temperature and improves cleanliness, it also wastes a significant amount of water.
Thus, there are unresolved issues with current wafer grinding techniques. What is needed is a method of conserving water supplied to the grinder during idle mode that will not adversely affect the temperature of the various grinding surfaces and components. What is further needed is a method that will adequately purge the grinder of any waste material whenever the grinder enters idle mode.